"I extend my sympathies to the woman's family during this very trying time," Heather Howard, commissioner of the state Department of Health and Senior Services, said in a statement. "Unfortunately, influenza is a serious disease and deaths are not unexpected."

The health department did not identify the woman nor provide her hometown or other information about her.

There are 21,449 confirmed cases of the novel flu virus in the United States, contributing to 87 deaths, according to the federal Centers for Disease Control and Prevention.

In New Jersey, there are now 568 confirmed cases of H1N1 influenza, affecting residents in 19 of the state's 21 counties, the state health department said today. In addition, 275 probable cases are being tested by the state laboratory.

In most cases, the illness has caused typical flu symptoms, including fever, cough, sore throat, chills and body ache, public health officials have said.

Nationally, about 70 percent of people requiring hospitalization with swine flu have had an underlying health condition, most often asthma or diabetes, said Daniel Jernigan, deputy director of the CDC's influenza division.

People with compromised immune systems or chronic heart disease are also at higher risk for severe illness, Jernigan said.

Stephen Smith, an infectious disease specialist at St. Michael's Medical Center in Newark, said people with these conditions are at higher risk for severe illness because their ability to clear their airways is compromised.

In New Jersey, four of the five people to die from the swine flue have had other, unspecified health issues.

The four are the Hudson County woman who died Friday; a 10-year-old boy from Sussex County, a 36-year-old man from Union County; and a 49-year-old man from West Orange. The state medical examiner's office is trying to determine whether the fifth person, a 15-year-old boy from Franklin Township, in Somerset County, had underlying health issues.

Public health officials are telling residents to protect themselves by washing their hands frequently with soap and water or hand sanitizer, covering their mouths when they cough or sneeze and staying home from work or school when ill.

"It is important for all New Jersey residents to remain vigilant and take proper precautions to protect themselves and their families," Howard said in the statement.